As an instant message system, an independent system has been established as can be seen in the AIM (AOL INSTANT MESSENGER) of AOL (Trade Mark) (AMERICA ONLINE (Trade Mark)), and the communication tool provided under the trademark MSN MESSENGER or YAHOO MESSENGER. In these systems, it has been impossible to realize communication, for example, between a user who uses the AIM and a user who uses the MSN MESSENGER or YAHOO MESSENGER because the mutual communication property is not yet established between these systems.
FIG. 11 is a system configuration diagram which illustrates practically the problems of the instant message system of the prior art. In the prior art system, since the connection ability between different systems is not yet established, it is impossible for the client terminals 4a, 4b belonging to different systems to realize the communication between the independent systems 1a, 1b. In addition to a problem that the common communication protocol is not yet provided for different systems, there exists a problem that a user A (terminal 4a) belonging to the system 1a and a user B (terminal 4b) belonging to the system 1b cannot detect the conditions of the partner with each other, because it is not yet possible to use in common or synchronize a user information collected by each system and a presence information of each user by transferring such information with each other.
The problems of the prior art illustrated in FIG. 11 are also described in the reference “Effect of Instant Messages in a Company” by Bin Ebitani (Nikkei Communications 2001, 11, 5; pp106-113).
The impp (Instant Messaging and Presence Protocol; protocol of instant message of which standardization work is progressed in the IETF) working group of IETF (Internet Engineering Task Force; Internet Technique Standardizing Committee) is planning to specify the standard specifications of the data format of presence information to be treated by the instant message system as an attempt to realize mutual connection between different instant message systems.
In order to realize mutual connection between the different instant message systems, not only the data format of information to be processed must be used in common but also a problem of how to transfer the information generated in each system to the other system must be solved.
In a practical example, it is required for a user of the AIM to know the presence information (on-line/off-line conditions) of a user having the account of the MSN messenger (communication tool of Microsoft Corp.) that the common sharing/synchronization of presence information of users must be realized among different systems.
However, common sharing of all information pieces by respective systems will require a storage device having a large amount of capacity and also require a large share in the management thereof. Moreover, even if it is not required to know the capacity of storage device and load of the management, when all information pieces are synchronized whenever the information is updated, communications between systems are generated frequently, resulting in a large amount of load on the communication apparatus and network.